Of course you can sign in without giving your email address. To sign in, you just type in your username and password. It's case sensitive. But if you want to sign up, you'll need to give an email address.

This is the discussion page for an anonymous user who has not created an account yet or who does not use it, identified by the user's numerical IP address.

Some IP addresses change periodically, and may be shared by several users. If you are an anonymous user, you may create an account or log in to avoid future confusion with other anonymous users. Registering also hides your IP address.